Hydraulic hammers are used on work sites to break up large hard objects before such objects can be moved away. Hydraulic hammers may be mounted to back hoes or excavators or other machines. Typically, the hammer assembly is powered by either a hydraulic or pneumatic pressure source or a combination of both. With those hammer assemblies powered by a combination of hydraulic and pneumatic pressure, a piston is retracted against a volume of compressible gas by applying a hydraulic fluid pressure to a first shoulder of a piston. As the piston retracts, the volume of gas decreases, increasing its pressure. Once the piston reaches a predetermined position, high pressure hydraulic fluid is applied to a second shoulder of a piston that drives the piston in a downward direction for a work or power stroke. The downward movement of the piston allows the compressed gas to expand, releasing energy which further propels the downward movement of the piston. The work tool strikes the object to be broken up. During the power stroke, the downward moving piston strikes a work tool, which, in turn, is driven in the downward direction. In order to provide the additionally energy released from the expansion of the compressed gas, the hammer assembly is pre-charged with the volume of compressed gas before operation.
German Patent Application to 102011088490A1 is directed to a device having a striker provided in a hammer pipe and accelerated by a pneumatic spring unit in an axial direction. The pneumatic spring unit includes three air chambers, which are separated from each other. A controllable valve element ventilates the air chambers of the pneumatic spring unit. One of the air chambers is arranged between a piston and a bottom of the hammer pipe in the axial direction. The other two air chambers partially form a pneumatic spring. However, no mechanism for self-charging the pneumatic spring is disclosed.